A stand-alone printer is commonly used in conjunction with a computer system in order to print images in the form of pictures, text, and/or graphics that may be displayed on a monitor of the computer system. A variety of technologies can be utilized by printers, including inkjet technology and electrophotographic, or laser, technology.
A printing process using inkjet technology involves moving an inkjet cartridge horizontally along a vertically moving print medium, such as a sheet of paper, and sequentially depositing ink by ejecting the ink onto the paper to form an image. For color inkjet printing, the inkjet cartridge includes jets that are connected to four ink reservoirs. The reservoirs contain cyan, magenta, yellow, or black ink. For grayscale printing, the inkjet cartridge typically includes a single reservoir of black ink.
A printing process using electrophotographic technology involves creating neutral regions on a positively charged drum, which represents a reverse image of the image to be printed. The drum is then dusted with positively charged particles, or toner. The toner is attracted to the neutral regions on the drum. When a negatively charged paper comes in contact with the drum, the attached toner transfers to the paper to form the image on the paper.
Regardless of the technology utilized, a conventional stand-alone printer is typically fed with a print medium in which an image is to be printed. The approach to feeding the print medium dictates the minimum size of the printer. For example, in order to print onto a paper of letter size, i.e. 21.59 cm.times.27.94 cm, a stand-alone printer must be at least 21.59 cm wide to accommodate the letter-size paper. Since print media must be fed into a stand-alone printer, an image cannot be printed onto a rigid paper or other print media that cannot be fed into the stand-alone printer.
A solution to the minimum size requirement of a conventional stand-alone printer and the limited types of print media that can be used to print an image is a hand-held printer that can be manually manipulated over a print medium. Because the print medium is not fed into the hand-held printer, the hand-held printer can be made much smaller than the stand-alone printers and can print on a greater variety of print media. U.S. Pat. No. 5,240,334 to Epstein et al. (hereinafter Epstein) describes a hand-held printer that is coupled to a host computer. The hand-held printer described in Epstein is an inkjet printer that can be used to print addresses on envelopes. The hand-held printer is used in conjunction with a base unit that has grooves to guide the printer during a printing process. The Epstein hand-held printer contains a mechanical device with a ball that rolls on the print medium during the printing process. The rotation of the ball is used to generate data for tracking the vertical and horizontal movement of the printer.
A concern with regard to the Epstein printer is that the ball used for tracking the printer may skid during the printing process. The effect of such skidding is to generate incorrect data relating to the movement of the printer. Another concern with the use of the ball for tracking is that the ball must be in constant contact with a print medium. If the hand-held printer of Epstein is temporarily removed from the print medium during a printing process, the hand-held printer must be placed back on the print medium at the precise location where the printing ceased in order to resume the printing process.
A similar inkjet hand-held printer is described in U.S. Pat. No. 5,311,208 to Burger et al. (hereinafter Burger) that is also connected to a host computer. The hand-held printer described in Burger includes a computer mouse that is integrated into the housing of the hand-held printer. In one embodiment, a support unit is utilized to guide the printer across a print medium in a horizontal direction. Similar to the printer described in Epstein, the hand-held printer of Burger also uses a mechanical device with a ball to track the printer movement during the printing process. The same concerns of Epstein are also present in the hand-held printer of Burger.
While the known hand-held printers operate well for their intended purpose, what is needed is an efficient hand-held printer with a non-mechanical tracking device.